This snapshot from the IMDB website has been retweeted around twitter today, with a still from Avatar on the left and one of Saoirse Ronan from The Lovely Bones on the right. Ronan is not connected to Avatar but it's impossible not to see the similarities in the two faces beyond the similarity of the composition.

I'm not accusing Cameron of stealing Ronan's likeness, but it is an interesting synchronicity. The bone structure looks similar, especially in the lighting in the picture with Ronan. Ronan is very lanky, so the comparison isn't unreasonable. I wonder if the guys at IMDB planned that, or it just happened.